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The impact of thickness and thermal annealing on refractive index for aluminum oxide thin films deposited by atomic layer deposition.

Wang ZY, Zhang RJ, Lu HL, Chen X, Sun Y, Zhang Y, Wei YF, Xu JP, Wang SY, Zheng YX, Chen LY - Nanoscale Res Lett (2015)

Bottom Line: The surface topography investigated by atomic force microscopy (AFM) revealed that the samples were smooth and crack-free.It is found that the refractive index of Al2O3 thin films decrease with increasing film thickness and the changing trend revised after annealing.A thickness transition is also found by transmission electron microscopy (TEM) and SE after 900°C annealing.

View Article: PubMed Central - PubMed

Affiliation: Shanghai Engineering Research Center of Ultra-Precision Optical Manufacturing, Department of Optical Science and Engineering, Laboratory of Micro and Nano Photonic Structures, Ministry of Education, Fudan University, Shanghai, 200433 China.

ABSTRACT
The aluminum oxide (Al2O3) thin films with various thicknesses under 50 nm were deposited by atomic layer deposition (ALD) on silicon substrate. The surface topography investigated by atomic force microscopy (AFM) revealed that the samples were smooth and crack-free. The ellipsometric spectra of Al2O3 thin films were measured and analyzed before and after annealing in nitrogen condition in the wavelength range from 250 to 1,000 nm, respectively. The refractive index of Al2O3 thin films was described by Cauchy model and the ellipsometric spectra data were fitted to a five-medium model consisting of Si substrate/SiO2 layer/Al2O3 layer/surface roughness/air ambient structure. It is found that the refractive index of Al2O3 thin films decrease with increasing film thickness and the changing trend revised after annealing. The phenomenon is believed to arise from the mechanical stress in ALD-Al2O3 thin films. A thickness transition is also found by transmission electron microscopy (TEM) and SE after 900°C annealing.

No MeSH data available.


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AFM images of 500 cycles Al2O3film. (a) As deposited and annealed at (b) 400°C, (c) 600°C, and (d) 900°C.
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Fig2: AFM images of 500 cycles Al2O3film. (a) As deposited and annealed at (b) 400°C, (c) 600°C, and (d) 900°C.

Mentions: The numbers of ALD cycles in the deposition were 50, 100, 300, and 500. Figure 2 shows the AFM images of selected ALD-Al2O3 thin film. The surface of the samples is smooth and crack-free, which indicates that Al2O3 films were well fabricated. The root mean square roughness (RMS roughness) information of all samples is listed in Table 1. The thickness of surface roughness layer used in SE fitting is fixed as the RMS value. And the roughness layer is described by a Bruggeman effective medium approximation mixed by 50% Al2O3 and 50% void [23].Figure 2


The impact of thickness and thermal annealing on refractive index for aluminum oxide thin films deposited by atomic layer deposition.

Wang ZY, Zhang RJ, Lu HL, Chen X, Sun Y, Zhang Y, Wei YF, Xu JP, Wang SY, Zheng YX, Chen LY - Nanoscale Res Lett (2015)

AFM images of 500 cycles Al2O3film. (a) As deposited and annealed at (b) 400°C, (c) 600°C, and (d) 900°C.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4384924&req=5

Fig2: AFM images of 500 cycles Al2O3film. (a) As deposited and annealed at (b) 400°C, (c) 600°C, and (d) 900°C.
Mentions: The numbers of ALD cycles in the deposition were 50, 100, 300, and 500. Figure 2 shows the AFM images of selected ALD-Al2O3 thin film. The surface of the samples is smooth and crack-free, which indicates that Al2O3 films were well fabricated. The root mean square roughness (RMS roughness) information of all samples is listed in Table 1. The thickness of surface roughness layer used in SE fitting is fixed as the RMS value. And the roughness layer is described by a Bruggeman effective medium approximation mixed by 50% Al2O3 and 50% void [23].Figure 2

Bottom Line: The surface topography investigated by atomic force microscopy (AFM) revealed that the samples were smooth and crack-free.It is found that the refractive index of Al2O3 thin films decrease with increasing film thickness and the changing trend revised after annealing.A thickness transition is also found by transmission electron microscopy (TEM) and SE after 900°C annealing.

View Article: PubMed Central - PubMed

Affiliation: Shanghai Engineering Research Center of Ultra-Precision Optical Manufacturing, Department of Optical Science and Engineering, Laboratory of Micro and Nano Photonic Structures, Ministry of Education, Fudan University, Shanghai, 200433 China.

ABSTRACT
The aluminum oxide (Al2O3) thin films with various thicknesses under 50 nm were deposited by atomic layer deposition (ALD) on silicon substrate. The surface topography investigated by atomic force microscopy (AFM) revealed that the samples were smooth and crack-free. The ellipsometric spectra of Al2O3 thin films were measured and analyzed before and after annealing in nitrogen condition in the wavelength range from 250 to 1,000 nm, respectively. The refractive index of Al2O3 thin films was described by Cauchy model and the ellipsometric spectra data were fitted to a five-medium model consisting of Si substrate/SiO2 layer/Al2O3 layer/surface roughness/air ambient structure. It is found that the refractive index of Al2O3 thin films decrease with increasing film thickness and the changing trend revised after annealing. The phenomenon is believed to arise from the mechanical stress in ALD-Al2O3 thin films. A thickness transition is also found by transmission electron microscopy (TEM) and SE after 900°C annealing.

No MeSH data available.


Related in: MedlinePlus